Double chimney

Can two gas fireplaces share the same chimney?

Having two gas fireplaces share the same chimney can be very convenient. However, having a shared chimney can create unforeseen health hazards if not properly planned.

What you need to know about chimneys and flues

The flue is a duct or pipe situated inside the chimney which provides a sealed pathway from the gas fire to the outside of a building. Metal flue pipes are often used for gas fires.

A chimney can have multiple flues, each flue venting a gas appliance, fireplace or other device. It’s important that the chimney is properly constructed to ensure the necessary spacing and sealant between the individual flues.

Flues are made of fire-resistant material which lines the inside of the flue, typically refractory concrete or impervious clay but sometimes metal.

All chimneys are required to be built with a flue lining to protect the masonry from combustion gases. The flue lining also improves the flow of the gases.

The damper is a pivoted or sliding metal flap in the flue that regulates the amount of draught and prevents excessive variations in air-flow. It can also close off the inside of the house from the outside, preventing heat loss.

Flues for gas fireplaces

Most gas fireplaces use a balanced flue that goes through the wall, just like a gas boiler. Another option is to use a powered flue, which allows the exhaust gas to be carried over longer routes with bends. Powered flues allow you more freedom as to where you place your gas fire, as they no longer have to be located near an external wall.

Shared chimney flues

Shared chimney flues mean that the flue for venting waste gases out of a building is shared among two appliances. If the construction is not done properly there is a danger of fire spread, combustion gas or carbon monoxide hazards.

Each appliance that produces combustion gases needs to have its own dedicated flue to vent combustion gases safely out of the building. If this is not the case, dangerous gases may be inadvertently conduction from one are of the building to another.

Shared fireplaces often share the same flue. It is also common for a single flue to serve both a heating appliance, such as a boiler or water heater, and a fireplace.

Can two gas fireplaces share the same chimney flue?

Two gas-fired appliances, such as a water heater and heating boiler, may be vented into the same chimney flue if your local authority approves of this installation.

If the gas appliances are on separate floors, there is a potential increased risk of fire or gas leaks between floors. Depending on the particular circumstances, additional installation requirements may be imposed, or sharing the same chimney flue may not be permitted.

If the chimney is an older, typically clay-lined, masonry construction, venting gas-fired heating equipment into it may be unsafe. The lower exhaust gas temperatures produced by gas-fired appliances may mean inadequate draft and risk fatal carbon monoxide poisoning of building occupants.

Before proceeding, it is advisable to seek the advice of your local fire officials and your local building control officer.

If you’re looking for advice on whether two gas fireplaces can share the same chimney, give us a call at Fiveways Fires & Stoves. Reach us by phone on 020 8127 4747 or via email at , and we’ll be delighted to answer all your questions.